A growing number of modern signboard ads feature vivid, sophisticated design logos and patterns, or images of products and human faces with photographic reality. In addition, a considerable number of signboards are now large in size, so that they can give strong impact on the viewers. General signboard production methods have been to cut letters out of colored sheets and attach them to generate logos, and to utilize various types of printing presses to create photographic images. As a result, signboard production has heretofore presented such problems as consuming a lot of time and labor, or requiring large-scale equipment such as a printing press.
Accordingly, there have been attempts to produce signboards featuring vivid images in a simpler way, by utilizing the inkjet method that permits printing of a design created on a personal computer directly onto a base material.
The inkjet method allows a wide range of base materials to be printed on, making it easy to print on both hard and soft material sheets such as papers, polymers and metals. Particularly when printing signboard ads that are installed outdoors and thus have a range of performance requirements including light weight, excellent strength and durability, resistance to rain, and affordable cost, the inkjet method presents a great advantage in that it makes it easy to print on polymer sheets that have these characteristics.
In addition, super-wide-format inkjet printers boasting a printing width of 2,000 mm or more are available of late and allowing large-size printed matter, which would otherwise require the traditional patchwork process, to be produced in one go. These printers, and other advancements, are making it even easier to produce signboards.
In general, tarpaulins are commonly used polymer sheets for signboard ads. For reference, a tarpaulin is a composite laminate sheet having a polyester or polyamide core material and whose top and bottom layers are each constituted by a polyvinyl chloride, ethylene-vinyl acetate copolymer, or other vinyl polymer.
Among the inkjet ink compositions printed on these composite sheets are non-aqueous inkjet ink compositions based on organic solvents (or more recently, environmentally-friendly organic solvents). Non-aqueous inkjet ink compositions require use of materials that offer good wettability, drying property, fixing property, etc., with respect to the polyvinyl chloride, ethylene-vinyl acetate copolymers, and other vinyl polymers traditionally used as surface materials for composite sheets.
Known methods to meet this requirement include: using an organic solvent constituted by an alkylene glycol monoether monoester and a cyclic ester (refer to Patent Literature 1); using a binder resin constituted by a vinyl polymer, as well as an organic solvent containing a specified quantity of an environmentally-friendly polyalkylene glycol dialkyl ether (refer to Patent Literature 2); and containing, as an organic solvent, a specified quantity of a diethylene glycol ethyl methyl ether and a specified quantity of a propylene carbonate (refer to Patent Literature 3).
However, in recent years there has been demand for higher printing speeds, and when traditional non-aqueous inkjet ink compositions (particularly non-aqueous inkjet ink compositions using environmentally-friendly organic solvents) are used for printing, the problems of insufficient filling of solid areas (hereinafter referred to as “solid fill property”), poor discharge stability, and mottling have arisen.